Functional fluids having increased fire resistance

ABSTRACT

PRODUCTION OF FUNCTIONAL FLUIDS, PARTICULARLY AIRCRAFT HYDRAULIC FLUIDS, OF IMPROVED FIRE RESISTANCE, COMPRISING A FUNCTIONAL FUID BASE STOCK, SUCH AS A PHOSPHATE ESTER, E.G., TRI-N-BUTYL PHOSPHATE, OR MIXTURES OF SUCH BASE STOCKS, AND A SMALL AMOUNT OF A SELENIUM OR TELLURIUM DIALKYL DITHIOCARBAMATE, E.G., SELENIUM TETRA (DIETHYL DITHIOCARBAMATE) OR ITS TELLURIUM ANALOGUE.

United States Patent Ofiice 3,733,276 FUNCTIONAL FLUIDS HAVING INCREASED FIRE RESISTANCE Robert S. McCord, Pacific Palisades, Donald H. Nail, Los Angeles, and Martin B. Sheratte, Reseda, Calif., assignors to McDonnell Douglas Corporation, Santa Monica, Calif. No Drawing. Filed May 3, 1971. Ser. No. 139,870

Int. Cl. C09k 3/00 US. Cl. 25278 26 Claims ABSTRACT OF THE DISCLOSURE Production of functional fluids, particularly aircraft hydraulic fluids, of improved fire resistance, comprising a functional fluid base stock, such as a phosphate ester, e.g., tri-n-butyl phosphate, or mixtures of such base stocks, and a small amount of a selenium or tellurium dialkyl dithiocarbamate, e.g., selenium tetra (diethyl dithiocarbamate) or its tellurium analogue.

This invention relates to functional fluid compositions having improved fire resistance and is particularly directed to compositions comprising certain functional fluids and an additive amount sufficient to improve fire resistance, of certain selenium or tellurium compounds.

Many different types of materials are employed as functional fluids and functional fluids are utilized in a wide variety of applications. Thus, such fluids have been utilized as electronic coolants, diffusion pump fluids, lubri cants, damping fluid, power transmission and hydraulic fluids, heat transfer fluids and heat pump fluids. A particularly important application of such functional fluids has been their utilization as hydraulic fluids and lubricants in aircraft, requiring successful operation of such fluids over a wide temperature range, a particularly important and highly desirable property of such fluids being fire resistance.

Functional and hydraulic fluids employed in many industrial applications and particularly hydraulic fluids for aircraft must meet a number of important requirements. Thus, such hydraulic fluids particularly for aircraft use, should be operable over a wide temperature range, should have good stability at relatively high temperatures and preferably have lubricating characteristics. In addition to having the usual combination of properties making it a good lubricant or hydraulic fluid, each fluid should also have relatively low viscosity at extremely low temperatures and an adequately high viscosity at relatively high temperatures, and must have adequate stability at the high operating temperatures of use. Further, it is of importance that such fluids be compatible with and not adversely affect materials including metals and non-metals such as elastomeric seals of the system in which the fluid is employed. It is particularly important in aircraft hydraulic fluids and lubricants that such fluids have as high a fire resistance as possible to prevent ignition if such fluids are accidentally or as result of damage to the hydraulic system, sprayed onto or into contact with surfaces or materials of high temperature.

While many functional and hydraulic fluid compositions have been developed having most of the aforementioned required properties, many of these compositions do not have the requisite high fire resistance desired particularly for use of such functional fluid or hydraulic fluid compositions in modern high speed aircraft or in a hydraulic system located near a high temperature jet-turbine power plant of a jet-turbine aircraft.

Thus, as an illustration, many functional and hydraulic fluids have an autoignition temperature ranging from about 450 to about 750 F. It is particularly desirable to 3,733,276 Patented May 15, 1973 increase the autoignition temperature of such functional and hydraulic fluids above 750 F., e.g., to the range of about 800 to about l,000 F.

It has now been found in accordance with the present invention that the fire resistance, or autoignition temperature, of functional fluid or hydraulic fluid compositions, can be significantly improved by the addition to such compositions of a small amount of certain selenium or tellurium compounds, in the form of selenium or tellurium dialkyl dithiocarbamates, defined in greater detail hereinafter. The inclusion of such selenium-containing or tellurium-containing additives in functional and hydraulic fluid compositions generally does not adversely affect any of the above noted important characteristics of such fluids, particularly aircraft hydraulic fluids, including their desirable viscosity characteristics.

Another important feature is that certain recently developed hydraulic fluids for aircraft use have been designed particularly to have reduced density, but many of these low density fluids have inferior fire resistance to the higher density hydraulic fluids, and it has been found that the selenium and tellurium-containing additives of the invention When incorporated into such low density fluids substantially increase the fire resistance and reduce the flammability of these low density hydraulic fluids.

The use of dialkyl selenides as oxidation inhibitors for orthosilicate fluids is described in US. Pat. 3,118,841 to Moreton. In such patent the selenide, e.g., dilauryl selenide, is employed in combination with other oxidation inhibitors such as phenyl alpha naphthylamine. However, selenides which inhibit oxidation in liquids do not necessarily function to reduce flammability, or to increase autogenous ignition temperature of a fluid, and in such patent only orthosilicates are employed as the base stock. Further, many of the selenides are toxic, thermally unstable, insufliciently soluble at the working temperature, or have an objectionable odor. Certain selenides also tend to corrode metals. Moreover, in order to effectively reduce flammability, selenium compounds should also possess the property of decomposing in the plasma condition in flames to prevent or poison continuation of the flame.

It has been found that certain selenium or tellurium dialkyl dithiocarbamates, as defined below, not only function to substantially increase autogenous ignition (autoignition) temperature and reduce flammability of a wide variety of functional fluids and hydraulic fluids, but in addition have the advantageous properties of being thermally stable, free from toxicity, relatively free from corrosion, do not have an objectionable odor, and have sufiicient solubility in most functional and hydraulic fluids to effectively function as flame inhibitors. In addition, the selenium and tellurium dialkyl dithiocarbamates employed according to the invention have no adverse effect on low temperature viscosity of the functional fluids, particularly when employed as hydraulic fluids in aircraft, do not adversely affect the thermal stability of the fluid, and are of relatively low cost.

Effective selenium and tellurium compounds, that is selenium and tellurium dialkyl dithiocarbamates, for use as additives in functional hydraulic fluids to reduce flammability and increase autoignition temperature of the fluid, according to the invention, preferably are selenium and tellurium tetra (dialkyl dithiocarbamate) compounds having the general formula:

where R and R each are alkyl, either straight chain or branched chain, of from about 1 to about 6 carbon atoms,

and R,, and R can be the same or different, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, n-amyl, isoamyl, n-hexyl, and the like; and where X is selenium or tellurium. Where R,, and R each contain more than 6 carbon atoms, solubility of the additives in the functional fluid is generally insutficient. Preferably R and R are the same alkyl group.

Specific examples of selenium dialkyl dithiocarbamate additives according to the invention are:

selenium tetra (dimethyl dithiocarbamate) selenium tetra (diethyl dithiocarbamate) selenium tetra (di-n-propyl dithiocarbamate) selenium tetra (diisopropyl dithiocarbamate) selenium tetra (di-n-butyl dithiocarbamatc) selenium tetra (diisobutyl dithiocarbamate) selenium tetra (di-n-amyl dithiocarbamate) (8) selenium tetra (diisoamyl dithiocarbamate) (9) selenium tetra (di-n-hexyl dithiocarbamate) (l0) selenium tetra (methyl ethyl dithiocarbamate) (l1) selenium tetra (ethyl isopropyl dithiocarbamate) (l2) selenium tetra (n-propyl isobutyl dithiocarbamate) tional fluid compositions of the present invention, and

the instant invention can be practiced utilizing the various modifications of the base stocks which are set forth below:

Preferably functional fluid base stocks are employed which are selected from the group consisting of phosphorus esters, amides of an acid of phosphorus, diand tricarboxylic acid esters, and petroleum hydrocarbons.

Phosphorus esters which can be employed according to the invention have the general formula:

where s, m and n can be 0 or 1, and not more than two of s, m and n can be 0, where R R and R each can be aryl such as phenyl and naphthyl, alkaryl such as cresyl, xylyl, ethyl phenyl, propyl phenyl, isopropyl phenyl, and the like, said aryl and alkaryl radicals preferably containing from 6 to about 8 carbon atoms, alkyl, both straight chain and branched chain of from about 3 to about 10 carbon atoms such as n-propyl, n-butyl n-amyl, n-hexyl, isopropyl, isobutyl, and the like, and alkoxy-alkyl having from about 3 to about 8 carbon atoms such as methoxy methyl, methoxy ethyl, ethoxy ethyl, methoxy propyl, and the like.

The corresponding phosphonates can also be employed, where one of s, m and n is O, and the corresponding phosphinates where two of s, m and n are 0.

Preferred phosphorus esters are the dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates.

Examples of such phosphate esters are the dialkyl aryl phosphates in which the alkyl groups are either straight chain or branched chain and contain from about 3 to about 10 carbon atoms, such as n-propyl, n-butyl, n-amyl, n-hexyl, isopropyl, isobutyl, isoamyl, and the aryl radicals have from 6 to 8 carbon atoms and can be phenyl, cresyl or xylyl, particularly dialkyl phenyl phosphates including dibutyl phenyl phosphate, butyl amyl phenyl phosphate, butyl hexyl phenyl phosphate, butyl heptyl phenyl phosphate, butyl octyl phenyl phosphate, diamyl phenyl phos- 4 phate, amyl hexyl phenyl phosphate, amyl heptyl phenyl phosphate, and dihexyl phenyl phosphate.

Examples of triaryl phosphates to which the selenides or tellurides of the invention can be added are those in which the aryl radicals of such phosphates have from 6 to 8 carbon atoms, that is, may be phenyl, cresyl or xylyl, and in which the total number of carbon atoms in all three of the aryl radicals is from 19 to 24, that is, in which the three radicals include at least one cresyl or xylyl radical. Examples of such phosphates include tricresyl, trixylyl, phenyl dicresyl and cresyl diphenyl phosphates.

Examples of trialkyl phosphates employed according to the invention include phosphates having alkyl groups which are either straight chain or branched chain With from about 3 to about 10 carbon atoms, such as npropyl n-butyl, n-amyl and n-hexyl, particularly tri-nbutyl phosphate, tri(2-ethyl hexyl) phosphate and triisononyl phosphate, the straight chain alkyl groups preferably containing from 4 to 6 carbon atoms.

Examples of alkyl diaryl phosphates which can be employed to produce the invention compositions include those in which the aryl radicals of such phosphates may have from 6 to 8 carbon atoms and may be phenyl, cresyl or xylyl, and the alkyl radical may have from about 3 to about 10 carbon atoms, examples of which are given above. Examples of the alkyl diaryl phosphates include butyl diphenyl, amyl diphenyl, hexyl diphenyl, heptyl diphenyl, octyl diphenyl, 6-methyl heptyl diphenyl, Z-ethylhexyl diphenyl, butyl phenyl cresyl, amyl phenyl xylyl, and butyl dicresyl phosphates.

Functional fluid base stocks according to the invention also include phosphonate and phosphinate esters having alkyl and aryl groups corresponding to those defined above with respect to the phosphate esters.

Examples of phosphinate esters to which the invention principles are applicable include phenyl-di-n-propyl phosphinate, phenyl-di-n-butyl phosphinate, phenyl-di-npentyl phosphinate, p-methoxyphenyldi-n-butyl phosphinate, tert-butylphenyl-di-n-butyl phosphinate. Examples of phosphonate esters to which the invention is applicable in clude aliphatic phosphonates such as an alkyl alkenyl phosphonate, e.g., dioctyl isooctene phosphonate, an alkyl alkane phosphonate such as di-n-butyl n-octane phosphonate, di-isooctyl pentane phosphonate, and dimethyl decane phosphonate, a mixed alkyl aryl phosphonate, for example, di-octyl phenyl phosph'onate di(n-amyl)phenyl phosphonate, di(n-butyl)phenyl phosphonate, phenyl butyl hexane phosphonate and butyl bisbenzene phosphonate.

Another class of phosphorus-containing compounds in which the additives of the invention can be employed as flame inhibitor are the amides of acids of phosphorus, e.g., amido phosphates, including the mono-, diand triamides of an acid of phosphorous, an example of which is phenyl N methyl N n butyl-N-methyl-N-n-butyl phosphorodiamidate. Additional examples are m-cresyl-p-cresyl-N,N-dimethylphosphoroamidate, di-m-cresyl-N,N-dimethylphosphoroamidate, di-p-cresyl-N,N-dimethyl-ph osphoroamidate, phenyl-N,N-dimethyl-N',N-dimethylphosphorodiamidate, N-methyl-N-butyl-N,N"-tetramethylphosphorotriam idate, N,N-di-n-propyl-N"-dimethylphosphorotriamidate.

Another class of functional fluid base stocks whose autoignition temperature can be improved by incorporporation of the selenides or tellurides of the invention are the di-and tricarboxylic acid esters, particularly the dicarboxylic acid esters. Preferred types of the latter compounds are the alkyl diesters of adipic and sebacic acid, that is the diester adipates and sebacates. Such esters can contain alkyl groups, either straight chain or branched chain, containing from about 4 to about 12 carbon 'atoms including butyl, isobutyl, amyl, pentyl, hexyl, isohexyl, nonyl, decyl and isodecyl groups. Specific examples of these base stocks are dihexyl, di 2-ethylhexyl, dioctyl, dinonyl, didecyl and diisodecyl adipate, and the correspondinng sebacates. Also, the diesters of the dicarboxylic aromatic acids, particularly the diesters of phthalic acid, that is the phthalate diesters can be employed as base stocks. The diesters of such acids can contain alkyl groups of from 4 to 12 carbon atoms, examples of which are given above with respect to the diesters of the dicarboxylic aliphatic acids, adipic and sebacic acid. Illustrative examples of the diester phthalates which can be employed are di-n-butyl phthalate, dihexyl phth'alate, dioctyl phthalate, dinonyl phthalate, didecyl phthalate, and diisodecyl phthalate.

There can also be employed as functional fluid base stocks according to the invention the esters of tricarboxylic acids, particularly the aromatic tricarboxylic acids such as trimellitic acid. The triesters of such acids can contain alkyl groups of from 4 to 12 carbon atoms, illustrative examples of which are noted above with respect to the dialkyl esters of phthalic acid, specific examples of trimellitate triesters including tri-butyl, tri-hexyl, tri-octyl, tri-isooctyl, trinonyl, tri-decyl and tri-isodecyl trimellitate.

There can also be ernployed as functional fluid base stocks to which the selenides or tellurides hereof are added according to the invention, petroleum hydrocarbons, which can contain carbon chains of from C to about C carbon atoms. A typical example of such a petroleum hydrocarbon is the red petroleum hydrocarbon liquid according to military specification MILH5606B, understood to contain carbon chains of about C to C carbon atoms, generally employed as a hydraulic fluid in military aircraft.

It is also contemplated within the scope of the present invention that mixtures of individual functional or hydraulic fluid components are included to form a single base stock. Thus, for example blends of esters of an acid of phosphorus can be employed, e.g., a blend of tri-n-butyl phosphate and tricresyl phosphate, blends of an ester of an acid of phosphorus and a dicarboxylic acid diester such as the aliphatic diesters of adipic, sebacic or phthalic acid, e.g., a mixture of tri-n-butyl phosphate and di-isodecyl adipate and/or di-isodecyl phthalate, or a combination or blend of dicarboxylic acid diesters and/ or tricarboxylic acid triesters can be employed, such as a blend of diisodecyl adipate and di-isodecyl phthalate.

Thus, there can be employed as functional fluid base stocks a blend or mixture of a phosphorus ester such as a phosphate and an alkyl diester of phthalic acid, with or without an alkyl diester of adipic acid and/or of sebacic acid, wherein said alkyl groups contain from about 4 to about 12 carbon atoms as described and claimed in the copending application, Functional Fluid Compositions, M. B. Sheratte, Ser. No. 129,270, filed Mar. 29, 1971. In addition, functional fluid base stocks can be utilized comprising a blend or mixture of a phosphorous esters such as a phosphate and an alkyl diester of adipic acid and/or of sebacic acid, as defined bove, and as described and claimed in the copending application, Functional Fluids, M. B. Sheratte, Ser. No. 129,269, filed Mar. 29, 1971.

The functional or hydraulic fluid base stocks employed and described above, can also contain other additives such as viscosity index improvers, in a small amount ranging from to about generally about 2 to about 10%, by weight of the composition. Examples of the latter are polyalkyl acrylates and methacrylates, the polyalkyl methacrylates generally being preferred, and in which the alkyl groups may contain from about 4 to about 12 carbon atoms, either straight or branched chain, and having an average molecular weight ranging from about 6,000 to about 15,000. Specific examples of such viscosity index im- 6 provers are polybutyl methacrylate and poly n-hexyl acrylate, having an average molecular weight between about 6,000 and about 12,000. Other additives such as corrosin inhibitors, stabilizers, metal deactivators, and the like, can also be employed.

For greatest effectiveness in substantially reducing the flammability, and for correspondingly substantially increasing the autoignition temperature of the above functional fluid base stocks according to the invention, it is usually desirable to employ only a small amount of the selenium dialkyl dithiocarbamate or tellurium dialkyl dithiocarbamate additive in the functional or hydraulic fluid base stock. Generally, there can be employed as little as 0.25% and up to about 5% of the selenide or telluride additive of the invention, preferably from about 0.5 to about 2% of such additive, in the functional fluid base stock, based on the weight of the composition. It has been found that an optimum amount of such selenide or telluride additive ranges from about 0.8 to about 2% by weight of the composition.

The selenium and telluride dialkyl dithiocarbamates employed as additives in functional fluids according to the invention can be prepared in known manner. Thus, for example, the selenium dialkyl dithiocarbamates can be prepared by reacting together in an alcoholic solution equivalent amounts of a secondary amine such as diethyl amine, with carbon disulfide and selenium dioxide. The selenium dialkyl dithiocarbamate precipitates as the reaction proceeds, and can readily be removered by filtration. The tellurium analogues can be prepared in similar manner by substituting tellurium dioxide for the selenium dioxide in the above procedure. These preparations follow the general procedure described in US. Pat. No. 2,347,128.

The following are examples illustrating practice of the invention by incorporation of the selenide or telluride additives according to the invention into functional fluid base stocks. In the examples below the term AIT means autoignition temperature, the autoignition temperature of the functional fluid compositions of the invention according to the examples below being determined in accordance with standard method of test for autoignition temperature in accordance with ASTM D2155 procedure. All percentages are in terms of percent by weight of the 0 functional fluid compositions.

EXAMPLE 1 To aliquot portions of tri-n-butyl phosphate, designated Fluid A in Table 1 below, is added varying minor amounts of selenium tetra (diethyl dithiocarbamate) and tellurium tetra (diethyl dithiocarbamate), and the autoignition temperature of the various aliquot portions of the resulting fluid compositions, and of a control of Fluid A with no such selenide or telluride additive, is obtained.

The results of such tests are noted in Table 1 below:

TAB LE 1 Additive eomtzen- TT tra ion A Fluid Additive (percent) 'F.)

A Selenium tetra (diethyl dithiocarbw mate). 0 730 A .do 0. 25 800 A tlo 0.5 825 A do 1. 0 860 A lo 1.5 805 A "(10... 2.0 895 A Tellugipm tetra (diethyl d 0.25 800 From Table 1 above, it is seen that incorporation of the above noted small amounts of the above selenide or telluride additive in Fluid A substantially increases the AIT of the control Fluid A from an AIT of 730 F.,

c.g., to 860 F. employing 1.0% of selenium tetra (diethyl dithiocarbamatc), and to 865 F. employing 1.0% of tellurium tetra (diethyl dithiocarbamate), and that increasing proportions of the selenide or telluride additive in the fluid generally increases the AIT thereof.

EXAMPLE 2 To aliquot portions of a blend of a functional fluid, designated Fluid B in Table 2 below and comprising about 80% tri-n-butyl phosphate, about 11% tricresyl phosphate, and a small amount of polybutyl methacrylate viscosity index improver, is added varying minor amounts of selenium tetra (diethyl dithiocarbamate) and tellurium tetra (diethyl dithiocarbamate) and the autoignition temperature of the various aliquot portions of the resulting fluid compositions and a control of Fluid B with no such additives, is obtained.

The results of such tests are noted in Table 2 below:

TABLE 2 Additive COIlQtl'ltration AIT Fluid Additive (percent) F.)

B Selenium tetra (diethyl dithiocarba- 740 mate From Table 2 above, it is seen that incorporation of the small amounts of the above noted selenide or telluride additive in Fluid B substantially increases the AIT of the control Fluid B from an AIT of 740 F., e.g., to 870 F. employing 1.0% of the selenide additive, and that increasing proportions of the selenide or telluride additive in the fluid generally increases the AIT thereof.

EXAMPLE 3 To respective portions of di-n-amyl pentane phosphonate fluid are added 2% of selenium tetra (diethyl dithiocarbamate) and 2% of tellurium tetra (diethyl dithiocarbamate) respectively, and the autoignition temperature of the resulting fluid compositions and of a control of such fluid in the absence of any selenide or telluride, is obtained.

The AIT of the fluids containing the 2% selenide or telluride additive noted above is in excess of about 750 F., substantially higher than the AIT of only 590 F. for the control fluid containing no selenide or telluride.

EXAMPLE 4 To a blend of a functional fluid containing about 70% di-isodecyl adipate and 30% tri-n-butyl phosphate are respectively added the selenide compounds (2), (3), (4), (5), and (9) above, and the corresponding tellurides, each in amounts respectively of 0.5, 1.0 and 1.8%, to respective portions of the functional fluid blend.

For each of these selenide and telluride additives incorporated in the functional fluid blend of this example, AIT is substantially increased in the range of about 800 to about 950 F., well above the less than 700 F. value for the control, in the absence of any selenide or telluride additive, and in each case for each of such additives, the AIT increases with increasing amount of additive incorporated, up to the 1.8% level.

EXAMPLE 5 The procedure of Example 1 is repeated, employing in place of Fluid A of Example 1, a functional fluid blend containing 70% di-isodecyl adipate and 30 tri-n-butyl phosphate.

Increases in AIT comparable to those of Example 1 are obtained.

EXAMPLE 6 The procedure of Example 1 is repeated, employing selenium tetra (diethyl dithiocarbamate) and its tellurium analogue in each of the following functional fluids, in each fluid varying the proportion of such selenide and telluride additives in the amounts noted in Example 1:

(l) A red petroleum hydrocarbon liquid containing hydrocarbon chains ranging from C to C (MILH 5606B).

(II) A blend of a functional fluid containing 50% di-isodecyl adipate, tri-n-butyl phosphate and 20% dibutyl phenyl phosphate.

(III) A blend of a functional fluid containing 50% di-isodecyl adipate, tri-n-butyl phosphate and 10% tri-isodecyl-tri-mellitate.

(IV) A blend of a functional fluid containing 39% tri-n-butyl phosphate, 47% di-isodecyl adipate and 10% di-isodecyl phthalate.

For each of the functional fluids (I), (II), (III), and (IV) above, incorporation of the above seleniumor tellurium-containing additive substantially increases AIT from that of the control, in the absence of any selenide additive, the AIT increasing in each case with increasing amount of such selenide or telluride additive incorporated, up to the 2.0% level, the incorporation of such additive in the above noted fluids (II), (III) and (IV) particularly increasing the AIT of such fluids from the 600 to 700 F. range to the 800 to 900 F. range.

EXAMPLE 7 The procedure of Example 1 is repeated employing in place of Fluid A of Example 1, phenyl-N-methyl-N-nbutyl-N'-methyl-N'-n-butyl phosphorodiamidate.

Results comparable to those of Example 1 are obtained.

In each of the Examples 1 to 7 above, a substantial improvement in autoignition temperature, and corresponding reduction in flammability is obtained, by incorporating the selenides or tellurides of the invention into the various functional fluids and blends thereof set forth in the examples, and such reduction in flammability is obtained without reducing the high temperature thermal stability of the functional fluid and without any increase in low temperature viscosity of the fluid, employing selected organo selenium and organo tellurium compounds having relatively good solubility in such fluids and high effectiveness therein, and which are relatively free from toxicity and are relatively odor-free.

From the foregoing, it is seen that the invention provides novel functional fluid compositions containing certain organo-selenium or organo-tellurium compounds which function efliciently as flame retardants or flame inhibitors in such fluids.

While we have described particular embodiments of our invention for purposes of illustration, it will be understood that various changes and modifications within the spirit of the invention can be made, and the invention is not to be taken as limited except by the scope of the appended claims.

We claim:

1. A functional fluid composition consisting essentially of a major portion of a functional fluid base stock selected from the group consisting of phosphorus esters, amides of an acid of phosphorus, diand tricarboxylic acid esters, and petroleum hydrocarbons containing carbon chains of from C to about C carbon atoms; and about 0.25 to about 5% by weight of said composition of a compound having the formula where R,.. and R each are alkyl of from about 1 to about 6 carbon atoms, and X is a member selected from the group consisting of selenium and tellurium, X being tellurium when said base stock is a petroleum hydrocarbon as aforesaid.

2. A composition as defined inclaim 1, said compound being present in an amount ranging from about 0.5 to about 2% by weight of said composition.

3. A composition as defined in claim. 1, wherein X is tellurium.

4. A composition as defined in claim 1, wherein said base stock is a phosphorus ester having the general formula:

where s, m and n are each an integer of to 1, and not more than two of s, m and n are 0, R R and R are each a member selected from the group consisting of aryl, alkaryl, alkyl of from about 3 to about carbon atoms, and alkoxyalkyl having from about 3 to about 8 carbon atoms.

5. A composition as defined in claim 1, said base stock comprising a petroleum hydrocarbon containing carbon chains of from C to about C 6. A functional fluid composition consisting essentially of a major portion of a functional fluid base stock selected from the group consisting of phosphorus esters, amides of an acid of phosphorus, diand tricarboxylic acid esters, and about 0.25 to about 5% by weight of such composition of a compound having the formula where R and R each are alkyl of from about 1 to about 6 carbon atoms, and X is a member selected from the group consisting of selenium and tellurium.

7. A composition as defined in claim 6, wherein X is selenium.

8. A composition as defined in claim 6, said compound being present in an amount ranging from about 0.5 to about 2% by weight of said composition and wherein X is selenium.

9. A functional fluid composition consisting essentially of a major portion of a functional fluid base stock, said base stock comprising a phosphate ester having the general formula:

where R R and R are each a member selected from the group consisting of aryl, alkaryl, alkyl of from about 3 to about 10 carbon atoms, and alkoxyalkyl having from about 3 to about 8 carbon atoms, and about 0.25 to about 5% by weight of said composition of a compound having the formula \N-CS- X II where R and R each are alkyl of from about 1 to about 10 6 carbon atoms, and X is a member selected from the group consisting of selenium and tellurium.

10. A composition as defined in claim 9, wherein said base stock comprises a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates.

11. A composition as defined in claim 9, wherein said base stock comprises a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates, and said compound is present in an amount ranging from about 0.5 to about 2% by weight of said composition.

12. A composition as defined in claim 9, wherein said base stock comprises a mixture of a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates, and a dicarboxylic acid ester.

13. A composition as defined in claim 12, wherein said dicarboxylic acid ester is selected from the group consisting of the alkyl diesters of adipic and sebacic acid, containing alkyl groups of from about 4 to about 12 carbon atoms.

14. A composition as defined in claim 12, wherein said dicarboxylic acid ester is an alkyl diester of phthalic acid containing alkyl groups of from about 4 to about 12 carbon atoms.

15. A composition as defined in claim 14, wherein said mixture includes a dicarboxylic acid ester selected from the group consisting of the alkyl diesters of adipic and sebacic acid, containing alkyl groups of from about 4 to about 12 carbon atoms.

16. A composition as defined in claim 9, wherein said base stock comprises a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates, and said compound is a member selected from the group consisting of selenium tetra (diethyl dithiocarbamate) and tellurium tetra (diethyl dithiocarbamate) 17. A composition as defined in claim 16, said compound being present in an amount ranging from about 0.5 to about 2% by weight of said composition.

18. A composition as defined in claim 9, wherein said base stock comprises a mixture of a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl and alkyl diaryl phosphates and a dicarboxylic acid diester selected from the group consisting of the alkyl diesters of adipic and sebacic acid, containing alkyl groups of from about 4 to about 12 carbon atoms, and said compound is a member selected from the group consisting of selenium tetra (diethyl dithiocarbamate) and tellurium tetra (diethyl dithiocarbamate).

19. A composition as defined in claim 9, said base stock comprising a mixture of a phosphate ester selected from the group consisting of dialkyl aryl, triaryl, trialkyl, and alkyl diaryl phosphates, and an alkyl diester of phthalic acid containing alkyl groups of from about 4 to about 12 carbon atoms, and said compound being a member selected from the group consisting of selenium tetra (diethyl dithiocarbamate) and tellurium tetra (diethyl dithiocarbamate).

20. A composition as defined in claim 19, wherein said mixture includes a dicarboxylic acid ester selected from the group consisting of the alkyl diesters of adipic and sebacic acid, containing alkyl groups of from about 4 to about 12 carbon atoms.

21. A composition as defined in claim 9, said base stock comprising a member selected from the group consisting of di-n-butyl phenyl phosphate, tri-n-butyl phosphate and tricresyl phosphate, and mixtures thereof, said compound being present in an amount ranging from about 0.5 to about 2% by weight of said composition.

22. A composition as defined in claim 21, said compound being a member selected from the group consisting of selenium tetra (diethyl dithiocarbamate) and tellurium tetra (diethyl dithiocarbamate) 11 12 23. A composition as defined in claim 21, said base References Cited stock comprising a mixture of tri-n-butyl phosphate and UNITED STATES PATENTS tricresyl phosphate.

2,685,502 8/1954 He1s1g 25233.6 X

24. A composition as defined in claim 21, said base stock including a member selected from the group con- 5 2,713,558 7/1955 schnlltz 252 33'6 sisting of diisodecyl adipate and diisodecyl phthalate, and 1:921091 8/1933 260 607 R X mixtures thereof.

25. A composition as defined in claim 21, said base MAYER WEINBLATTPnmary Exammer stock including a mixture of di-isodecyl phthalate and di- HARRIS A. PlTLICK, Assistant Examiner isodecyl adipate. 10

26. A composition as defined in claim 21, said base U.S. C1.X.R. stock being a mixture of tri-n-butyl phosphate, diisodecyl 260 666 5 989 adipate and diisodecyl phthalate. 

